fix streaming crash when canvas video pipeline isn't initialized by summeroff · Pull Request #1710 · streamlabs/obs-studio-node

summeroff · 2026-05-26T21:31:51Z

Summary

Fixes the Sentry-reported EXCEPTION_ACCESS_VIOLATION_READ at osn::SimpleStreaming::UpdateEncoders (osn-simple-streaming.cpp:302), and the equivalent latent crash in AdvancedStreaming::UpdateEncoders (osn-advanced-streaming.cpp:391).

Root cause

obs_get_video() unconditionally dereferences obs->data.main_canvas->mix->video. When obs_reset_video fails at app startup (e.g. when D3D11 returns DXGI_ERROR_DEVICE_REMOVED / DXGI_ERROR_DEVICE_HUNG during initial texture creation), obs_canvas_clear_mix has already set canvas->mix = NULL, and the failed obs_create_video_mix leaves it that way. On Go-Live, UpdateEncoders calls obs_get_video() and crashes.

The original Sentry report's OBS log shows the textbook sequence — 4× failed SetVideoContext with result: -1 and Device Removed Reason: 887A0006 — followed immediately by the SimpleStreaming::Create … Start chain.

Changes

osn-simple-streaming.cpp / osn-advanced-streaming.cpp:
- UpdateEncoders switches from obs_get_video() (main-canvas, unguarded) to obs_video_mix_get(this->GetCanvas(), mode) + obs_video_mix_get_video(mix) — canvas-scoped and NULL-safe. Falls back to VIDEO_FORMAT_NV12 when video is unavailable, which the existing switch already treats as the default.
- Start gains a defense-in-depth guard: if the streaming canvas has no video mix, return ErrorCode::CriticalError with a clear message rather than letting UpdateEncoders get there.
obs-studio-client/source/video.cpp:
- osn::Video::set now calls ValidateResponse after the SetVideoContext IPC call. Previously the server returned ErrorCode::Error on failure but the client dropped it on the floor, leaving JS with no way to know the video context never came up. Pairs with the desktop-side change below.

Pairs with

surface video-context init failures so UI can gate streaming desktop#5941 (fix_streaming_crash_no_video) — the desktop side needs this PR's IPC error to escape to JS. The desktop change is inert without this PR; this PR is useful on its own (the crash guard works regardless).

Deferred / out of scope

nodeobs_service.cpp:2222 and nodeobs_autoconfig.cpp:1072 also call unguarded obs_get_video() — same pattern, separate audit.
Automatic device_rebuild() on SetVideoContext failure would actually recover from transient device-removed; tracked as a follow-up.

Test plan

obs-studio-server and obs-studio-client both build clean on Windows (cmake RelWithDebInfo, exit 0).
Smoke test SimpleStreaming Start/Stop on a healthy machine — no regression.
Reproduce the device-removed path (TDR via NVIDIA Nsight or unplug/replug primary GPU mid-init) and verify Start returns CriticalError instead of crashing.
Verify ValidateResponse change doesn't surface false errors during normal startup flow.

🤖 Generated with Claude Code

obs_get_video() unconditionally dereferences main_canvas->mix->video. When obs_reset_video fails at startup (e.g. DXGI_ERROR_DEVICE_REMOVED during initial texture creation), canvas->mix is left NULL and the next SimpleStreaming::Start crashes here -- seen in Sentry crashing osn::SimpleStreaming::UpdateEncoders at osn-simple-streaming.cpp:302 with EXCEPTION_ACCESS_VIOLATION_READ. - Switch SimpleStreaming/AdvancedStreaming UpdateEncoders to obs_video_mix_get(GetCanvas(), mode) + obs_video_mix_get_video(mix), which is canvas-scoped and NULL-safe. - Add a NULL-mix guard in both Start handlers so we return a clean CriticalError instead of crashing if the canvas video never came up. - Make osn::Video::set propagate IPC errors via ValidateResponse so SetVideoContext failures reach the JS layer instead of being silently dropped. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

The canvas-video lookup in UpdateEncoders / Start was open-coded four times across SimpleStreaming and AdvancedStreaming. Each site also had to know that osn::Output::GetCanvas() returns obs_video_info* (the osn "canvas") rather than libobs's obs_canvas_t -- which is easy to miss since the libobs API obs_canvas_get_video() takes the latter. Hide the juggling behind one helper on the Output base class that takes a rendering mode and returns a video_t* (or NULL when the canvas video mix isn't ready). Call sites collapse to a single readable line, and future callers don't have to re-discover the type mismatch. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Copilot

Pull request overview

This PR hardens streaming start/update logic against cases where the OBS video pipeline (canvas video mix) was not successfully initialized (e.g., GPU/device lost during startup), preventing null-dereference crashes and surfacing IPC errors back to the JS layer.

Changes:

Simple/Advanced streaming: replace obs_get_video() usage in UpdateEncoders() with canvas-scoped video lookup and add a start-time guard that returns a CriticalError when no canvas video mix exists.
Server: add Output::GetCanvasVideo(mode) helper to centralize canvas→mix→video lookup.
Client: propagate SetVideoContext IPC failures via ValidateResponse so initialization errors are observable in JS.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
obs-studio-server/source/osn-simple-streaming.cpp	Use canvas-scoped video output in `UpdateEncoders()`; fail fast in `Start()` when no video mix exists.
obs-studio-server/source/osn-advanced-streaming.cpp	Same crash-avoidance pattern as SimpleStreaming for advanced mode.
obs-studio-server/source/osn-output.hpp	Declare `Output::GetCanvasVideo()` helper API.
obs-studio-server/source/osn-output.cpp	Implement `Output::GetCanvasVideo()` helper.
obs-studio-client/source/video.cpp	Add `ValidateResponse` handling for `SetVideoContext` IPC call.

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+video_t *osn::Output::GetCanvasVideo(obs_video_rendering_mode mode)
+{
+	return obs_video_mix_get_video(obs_video_mix_get(m_canvas, mode));


Match the pattern in osn-video.cpp: return nullptr when the mix lookup fails instead of dereferencing it. Without this, the helper crashes in exactly the scenario this PR targets (no canvas video mix), defeating the Start() guards that call it. Also apply clang-format-13 fixes flagged by CI. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

summeroff mentioned this pull request May 26, 2026

surface video-context init failures so UI can gate streaming streamlabs/desktop#5941

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summeroff requested a review from Copilot May 27, 2026 16:09

Copilot started reviewing on behalf of summeroff May 27, 2026 16:10 View session

Copilot AI reviewed May 27, 2026

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Comment thread obs-studio-server/source/osn-output.cpp Outdated

video_t *osn::Output::GetCanvasVideo(obs_video_rendering_mode mode)

{

return obs_video_mix_get_video(obs_video_mix_get(m_canvas, mode));

summeroff merged commit e308a1b into staging May 27, 2026
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fix streaming crash when canvas video pipeline isn't initialized#1710

fix streaming crash when canvas video pipeline isn't initialized#1710
summeroff merged 3 commits into
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fix_streaming_crash_no_video

summeroff commented May 26, 2026 •

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summeroff commented May 26, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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summeroff commented May 26, 2026 •

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